In a small bowl, mix chopped basil, vinegar, mustard, honey, and garlic. Whisking, blend in oil.
Thread zucchini on thin skewers so rounds lie flat and pieces touch. Brush generously with basil vinaigrette.
Place zucchini on a barbecue grill over a solid bed of medium coals or medium heat on a gas grill (you can hold your hand at grill level only 4 to 5 seconds). Close lid on gas grill. Cook until brown on each side, 5 to 7 minutes total; turn once.
Push zucchini from skewers onto a platter. Drizzle with remaining vinaigrette. Garnish with basil sprigs. Add salt and pepper to taste.